A conventional method for producing a fatty alcohol comprises catalytically reducing a starting material selected from among natural fats and oils, fatty acids and fatty acid esters to thereby obtain a fatty alcohol. This reaction is to be performed in the presence of a hydrogenation catalyst under a pressure of 250 to 300 bar at a temperature of 200.degree. C. or above under an excess hydrogen atmosphere.
In the method disclosed in West Germany Patent DE-2613226, a starting material (coconut oil methyl ester) is preliminarily gasified and then an alcohol is produced using two fixed bed reactors connected in series.
Since the reduction of a fatty acid ester, a fatty acid triglyceride or a fatty acid is an exothermic reaction, when an alcohol is produced by catalytically reducing these starting materials in a fixed bed reactor, the reaction has been carried out under apparently isothermal conditions with liberating the heat generated during the course of the reaction in the reactor in order to improve qualities of the alcohols thus produced, as disclosed in JP-A-64-47725 (corresponding to U.S. Pat. No. 5,043,485), JP-A-64-47726 (corresponding to EP-A-0300346), JP-A-63-39829 (corresponding to U.S. Pat. No. 4,942,020) and JP-A-1-275542 (corresponding to U.S. Pat. No. 4,942,266) (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and U.S. Pat. No. 4,855,273 and U.S. Pat. No. 4,935,556.
When a hydrogenation reaction is effected at a usual reaction temperature in a method for producing a fatty alcohol, the reaction would excessively proceed and thus by-products (for example, hydrocarbons, aldehydes) are formed. Since the reduction of a fatty acid ester, a fatty acid triglyceride or a fatty acid is an exothermic reaction, during the reduction of these starting materials, the temperature in a reactor increases to more than that of the reactor inlet. In this case, therefore, it is difficult to reduce the amount of these by-products by controlling the reaction temperature in a single reactor. In the above-mentioned JP-A-64-47725 (corresponding to U.S. Pat. No. 5,043,485), JP-A-64-47726 (corresponding to EP-A-0300346) and JP-A-1-275542 (corresponding to U.S. Pat. No. 4,942,266) and U.S. Pat. No. 4,855,273 and U.S. Pat. No. 4,935,556, the reaction is performed in a single reactor under approximately isothermal conditions. Accordingly, the amount of the by-products can hardly be reduced.
Further, it is required to eliminate hydrocarbons or aldehydes formed by the excessive reaction, since the qualities of the alcohol are deteriorated by these byproducts. The boiling point ranges of the hydrocarbons overlap these of short-chain alcohols and thus the starting material must be fractionated by, for example, distillation prior to the reaction.
On the other hand, the aldehydes are converted into fatty alcohols of the corresponding chain length by treating with a chemical, i.e., a reducing agent.
However, these treatments are disadvantageous in that they make the procedure complicated and cause an increase in the production cost.
In DE-2613226, the starting material for producing an alcohol is gasified and the reaction is performed by using two reactors. However the gas phase reaction makes it further difficult to control the temperatures in the reactors and an amount of hydrocarbon by-products, in particular, formed during the reaction increases. In addition, the reaction temperature in each reactor is not specified in this patent and, therefore, the object of the use of the two reactors is unclear.